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Barcelona and its metropolitan area has a humid subtropical climate (Köppen climate classification: Cfa), bordering a Mediterranean climate (Csa) with mild winters and hot summers. According to Troll-Paffen climate classification, Barcelona has a warm-temperate subtropical climate (Warmgemäßigt-subtropisches Zonenklima). According to Siegmund/Frankenberg climate classification, Barcelona has a subtropical climate. Barcelona is located on the eastern coast of the Iberian Peninsula, so Atlantic west winds often arrive in Barcelona with low humidity, producing no rain. The proximity of the Atlantic, its latitude, and the relief, are the reasons why the summers are not as dry as in most other Mediterranean Basin locations.
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General
Its average annual temperature is 21.2 °C (70.2 °F) during the day and 14.1 °C (57.4 °F) at night. In the coldest month – January, typically the temperature ranges from 12 to 16 °C (54 to 61 °F) during the day and 6 to 10 °C (43 to 50 °F) at night. In the warmest month – August, the typically temperature ranges from 28 to 32 °C (82 to 90 °F) during the day and about from 20 to 24 °C (68 to 75 °F) at night. Large fluctuations in temperature are very rare.
Winter
Winters in Barcelona are mild. December, January and February are the coldest months, with average temperatures around 16 °C (61 °F) during the day and 10 °C (50 °F) at night. Slight frost at night is more common on the hills around the city and in the outer metropolitan area (far from the sea, like in Montjuic). Frost during the day has been recorded in the city and inner metropolitan area during the strongest cold waves and snowstorms, but it's very rare. The last time when the city recorded a temperature below freezing, it was during the January 1985 cold wave.
Summer
Generally the summer season lasts about six months, from May to October. July and August are the warmest months, with average temperatures around 28–29 °C (82–84 °F) during the day and 22–23 °C (72–73 °F) at night. In June and September the average temperature is around 26 °C (79 °F) during the day and 20 °C (68 °F) at night, and in May and October the average temperature is around 22–23 °C (72–73 °F) during the day and 16–17 °C (61–63 °F) at night. Daytime temperatures above 34 °C (93 °F) are rare.
Transitional months
Two months – April and November – are transitional, with the temperature sometimes exceeding 20 °C (68 °F), and an average temperature of 17–18 °C (63–64 °F) during the day and 8–9 °C (46–48 °F) at night.
Sunshine
Sunshine duration is 2,524 hours per year, from 138 - average 4.5 hours of sunshine per day in December to 310 - average 10 hours of sunshine per day in July. This is the middling value for the southern half of Europe because in this part of the continent, sunshine duration varies from about 2,000 to about 3,000 hours per year. However, this is 60% larger value than in northern half of Europe, where sunshine duration is around 1500 hours per year. In winter Barcelona has about three times (150%) more sun duration than in the northern half of Europe.
Daylight
Barcelona enjoys one of the most optimal number of hours of winter daylight in Europe. Days in winter are not as short as in the northern part of the continent, the average hours of daylight in December, January and February is 10 hours (for comparison: London or Moscow or Warsaw - about 8 hours).
Precipitation
Barcelona has on average only 55 precipitation days a year, therein average several rainy days per month (≥ 1 mm), ranging from 2 in July to 6 in October. The average annual precipitation is less than 640 mm (25 inches), ranging from 20 mm (0.79 inch) in July to 91 mm (3.58 inch) in October.
Humidity
Average relative humidity is 72%, ranging from 69% in July to 75% in October.
Snow
Snowfalls are very rare, but slight frost at night is more common on the hills around the city and in the depths of the metropolitan area (far from the sea). Two heavy snowfalls occurred in Christmas 1962, and according to old news sources, in 1887. In the twenty-first century snow has fallen on 23 February 2013, 2 February 2012, 8 March 2010, 14 February 2010, 6 January 2009, 27 January 2006, 28 February 2005, 29 February 2004, 18 February 2003 and 14 December 2001. So, almost each winter could snow once especially in February.
Temperature extremes
The highest temperature recorded during the day is 37.4 °C (99.3 °F) on the 27 August 2010. On the August 2003 reported record, the average maximum temperature during the day was 32.8 °C (91.0 °F). The coldest temperature recorded was −8.0 °C (17.6 °F) at night on 27 December 1962.
Fog
Barcelona is generally a sunny city, however, some days of fog and spells of overcast days are not rare. Sea fog is frequent in early spring, when the first warm African air masses come in over the cold sea water.
Thunderstorms
Thunderstorms, which occasionally reach severe limits, are common from mid July until November. The most recent major summer storm was on the 31 July 2002, when over 200 mm (7.87 in) of rain were recorded at some observatories.
Winds
Though Barcelona is normally not a windy city, it is affected by sea breezes from May/June to September and winds from the west and northwest in winter. Eastern gales sometimes cause floods on the coastline. East and northeast winds can exceed 100 km/h (62.14 mph). In winter Barcelona is sometimes affected by the tramontana or mistral winds, like other places in the Northwestern Mediterranean Basin.
Sea temperature
Average annual temperature of sea is about 18 °C (64 °F). In the coldest month – January, the average sea temperature is 13 °C (55 °F). In the warmest month – August, the average sea temperature is 25 °C (77 °F).
Seasonal information
Because of the mild temperatures, much of the vegetation (palm species for example) remains green throughout the year, while the leaves of many deciduous trees do not fall until February. New leaves appear in March. Snow is rare in Barcelona (falling only once every two years on average), although there are resorts for winter sports in the Pyrenees 100–150 km from the city. Because of the climate and geographical location, the city hopes to host the 2026 Winter Olympics. The opening and closing ceremonies, medal ceremonies and indoor sports would be held in Barcelona, while outdoor sports would be held in ski resorts in the Pyrenees, mainly La Molina. Summers in Barcelona area are long and warm. Summer temperatures - above 20 °C (68 °F) - begin as early as April, although in this month the sea temperature is still cool: about 15 °C (59 °F). The summer season ends in October, although even in November temperatures can often exceed 20 °C (68 °F) and the sea temperature remains mild - 17 °C (63 °F). Over the summer season (6 months), the average temperatures is 21–28 °C (70–82 °F) during the day and the average sea temperature is 22 °C (72 °F). The weather in Barcelona during spring and autumn can be very changeable. During these months it can rain for quite long periods, but consecutive sunny days are also fairly common. The difference between temperatures during day and night is about 10-15 °C (20-30 °F).